Which Planet Has The Longest Day? - Universe Today Universe Today Which Planet Has The Longest Day? Article Updated: 19 Aug , 2016 by Jerry Coffey Just to be clear, this answer to ‘which planet has the longest day’ is based on this criteria: a planets day is how long it takes it to complete one rotation on its axis. This is also referred to as its rotational period. So, Venus has the longest day of any planet in our solar system. It completes one rotation every 243 Earth days. Its day lasts longer than its orbit. It orbits the Sun every 224.65 Earth days, so a day is nearly 20 Earth days longer than its year. Length Of A Day On The Planets In Our Solar System Mercury: 58 days and 15 hours Venus: 243 days Mars: 24 hours, 39 minutes and 35 seconds Jupiter: 9.9 hours Saturn: 10 hours 45 minutes 45 seconds, but can only be approximated because of atmospheric density.

Uranus: 17 hours, 14 minutes and 24 seconds Neptune: 16 hours, 6 minutes and 36 seconds, but it is a bit more complicated than that. The equator and poles rotate at different speeds. You would have to do more research on the planet to fully understand the varying day on Neptune. Now, back to why the Venusian day is longer than its year. Venus is closer to the Sun; therefore, its orbit takes a shorter period of time than its rotation upon its axis. The planet also rotates in retrograde. That means it spins in the opposite direction of the Earth. If you were standing on Venus, you could see the Sun rise in the West and set in the East. A manned Venus flyby mission was proposed in the late 1960s. The mission was planned to launch in late October or early November 1973, and would have used a Saturn V rocket to send three men. The flight would have lasted approximately one year. The spacecraft would have passed approximately 5,000 km from the surface about four months into the flight.

There have been several unmanned probes and flybys of the planet, including MESSENGER and the Venus Express. Future proposed missions include the BepiColombo, Venus InSitu Explorer, and the Venera-D. If you’d like more information on Venus, check out Hubblesite’s News Releases about Venus , and here’s a link to NASA’s Solar System Exploration Guide on Venus . We’ve also recorded an entire episode of Astronomy Cast all about Venus. Listen here, Episode 50: Venus . How Long Is A Day On The Other Planets Of The Solar System? - Universe Today Universe Today How Long Is A Day On The Other Planets Of The Solar System? Article Updated: 24 Jan , 2016 by Matt Williams Here on Earth, we tend to take time for granted, never suspected that the increments with which we measure it are actually quite relative. The ways in which we measure our days and years, for example, are actually the result of our planet’s distance from the Sun, the time it takes to orbit, and the time it takes to rotate on its axis. The same is true for the other planets in our Solar System.

While we Earthlings count on a day being about 24 hours from sunup to sunup, the length of a single day on another planet is quite different. In some cases, they are very short, while in others, they can last longer than years – sometimes considerably! Let’s go over how time works on other planets and see just how long their days can be, shall we? A Day On Mercury: Mercury is the closest planet to our Sun, ranging from 46,001,200 km at perihelion (closest to the Sun) to 69,816,900 km at aphelion (farthest). Since it takes 58.646 Earth days for Mercury to rotate once on its axis – aka. its sidereal rotation period – this means that it takes just over 58 Earth days for Mercury to experience a single day. However, this is not to say that Mercury experiences two sunrises in just over 58 days. Due to its proximity to the Sun and rapid speed with which it circles it, it takes the equivalent of 175.97 Earth days for the Sun to reappear in the same place in the sky.

Hence, while the planet rotates once every 58 Earth days, it is roughly 176 days from one sunrise to the next on Mercury. Images of Mercury’s northern polar region, provided by MESSENGER. Credit: NASA/JPL What’s more, it only takes Mercury 87.969 Earth days to complete a single orbit of the Sun (aka. its orbital period). This means a year on Mercury is the equivalent of about 88 Earth days, which in turn means that a single Mercurian (or Hermian) year lasts just half as long as a Mercurian day. What’s more, Mercury’s northern polar regions are constantly in the shade. This is due to it’s axis being tilted at a mere 0.034° (compared to Earth’s 23.4°), which means that it does not experience extreme seasonal variations where days and nights can last for months depending on the season. On the poles of Mercury, it is always dark and shady. So you could say the poles are in a constant state of twilight.

A Day On Venus: Also known as “Earth’s Twin”, Venus is the second closest planet to our Sun – ranging from 107,477,000 km at perihelion to 108,939,000 km at aphelion. Unfortunately, Venus is also the slowest moving planet, a fact which is made evident by looking at its poles. Whereas every other planet in the Solar System has experienced flattening at their poles due to the speed of their spin, Venus has experienced no such flattening. Venus has a rotational velocity of just 6.5 km/h (4.0 mph) – compared to Earth’s rational velocity of 1,670 km/h (1,040 mph) – which leads to a sidereal rotation period of 243.025 days. Technically, it is -243.025 days, since Venus’ rotation is retrograde. This means that Venus. rotates in the direction opposite to its orbital path around the Sun. The planet Venus, as imagined by the Magellan 10 mission.

Credit: NASA/JPL So if you were above Venus’ north pole and watched it circle around the Sun, you would see it is moving clockwise, whereas its rotation is counter-clockwise. Nevertheless, this still means that Venus takes over 243 Earth days to rotate once on its axis, which means that many, many days pass between one sunrise and the next. This may seem odd, until you consider that a single Venusian (or Cytherean) year works out to 224.701 Earth days. Yes, Venus takes a little more than 224 days to complete a single orbital period, but over 243 days to experience a single day and night cycle. So basically, a single Venusian day is longer than a Venusian year! Good thing Venus has other things in common With Earth, because it is sure isn’t its diurnal cycle! A Day On Earth: When we think of a day on Earth, we tend to think of it as a simple 24 hour interval. In truth, it takes the Earth exactly 23 hours 56 minutes and 4.1 seconds to rotate once on its axis.

Meanwhile, on average, a solar day on Earth is 24 hours long, which means it takes that amount of time for the Sun to appear in the same place in the sky. Between these two values, we say a single day and night cycle lasts an even 24. At the same time, there are variations in the length of a single day on the planet based on seasonal cycles. Due to Earth’s axial tilt, the amount of sunlight experienced in certain hemispheres will vary. The most extreme case of this occurs at the poles, where day and night can last for days or months depending on the season. At the North and South Poles during the winter, a single night can last up to six months, which is known as a “polar night”. During the summer, the poles will experience what is called a “midnight sun”, where a day lasts a full 24 hours. So really, days are not as simple as we like to imagine. But compared to the other planets in the Solar System, time management is still easier here on Earth. A Day On Mars: In many respects, Mars can also be called “Earth’s Twin”.

In addition to having polar ice caps, seasonal variations , and water (albeit frozen) on its surface, a day on Mars is pretty close to what a day on Earth is. Essentially, Mars takes 24 hours 37 minutes and 22 seconds to complete a single rotation on its axis. This means that a day on Mars is equivalent to 1.025957 days. The seasonal cycles on Mars, which are due to it having an axial tilt similar to Earth’s (25.19° compared to Earth’s 23.4°), are more similar to those we experience on Earth than on any other planet. As a result, Martian days experience similar variations, with the Sun rising sooner and setting later in the summer and then experiencing the reverse in the winter. However, seasonal variations last twice as long on Mars, thanks to Mars’ being at a greater distance from the Sun. This leads to the Martian year being about two Earth years long – 686.971 Earth days to be exact, which works out to 668.5991 Martian days (or Sols).

As a result, longer days and longer nights can be expected last much longer on the Red Planet. Something for future colonists to consider! Sunrise at Gale Crater on Mars. Gale is at center top with the mound in the middle, called Mt. Sharp (Aeolis Mons.) A Day On Jupiter: Given the fact that it is the largest planet in the Solar System, one would expect that a day on Jupiter would last a long time. But as it turns out, a Jovian day is officially only 9 hours, 55 minutes and 30 seconds long, which means a single day is less than a third the length of an Earth day. This is due to the gas giant having a very rapid rotational speed, which is 12.6 km/s (45,300 km/h, or 28148.115 mph) at the equator. This rapid rotational speed is also one of the reasons the planet has such violent storms. Note the use of the word officially. Since Jupiter is not a solid body, its upper atmosphere undergoes a different rate of rotation compared to its equator.

Basically, the rotation of Jupiter’s polar atmosphere is about 5 minutes longer than that of the equatorial atmosphere. Because of this, astronomers use three systems as frames of reference. System I applies from the latitudes 10° N to 10° S, where its rotational period is the planet’s shortest, at 9 hours, 50 minutes, and 30 seconds. System II applies at all latitudes north and south of these; its period is 9 hours, 55 minutes, and 40.6 seconds. System III corresponds to the rotation of the planet’s magnetosphere, and it’s period is used by the IAU and IAG to define Jupiter’s official rotation (i.e. 9 hours 44 minutes and 30 seconds) Jupiter and Io capturing the Sun. Image Credit: NASA/JPL So if you could, theoretically, stand on the cloud tops of Jupiter (or possibly on a floating platform in geosynchronous orbit), you would witness the sun rising an setting in the space of less than 10 hours from any latitude. And in the space of a single Jovian year, the sun would rise and set a total of about 10,476 times.

A Day On Saturn: Saturn’s situation is very similar to that of Jupiter’s. Despite its massive size, the planet has an estimated rotational velocity of 9.87 km/s (35,500 km/h, or 22058.677 mph). As such Saturn takes about 10 hours and 33 minutes to complete a single sidereal rotation, making a single day on Saturn less than half of what it is here on Earth. Here too, this rapid movement of the atmosphere leads to some super storms , not to mention the hexagonal pattern around the planet’s north pole and a vortex storm around its south pole. And, also like Jupiter, Saturn takes its time orbiting the Sun. With an orbital period that is the equivalent of 10,759.22 Earth days (or 29.4571 Earth years), a single Saturnian (or Cronian) year lasts roughly 24,491 Saturnian days. However, like Jupiter, Saturn’s atmosphere rotates at different speed depending on latitude, which requires that astronomers use three systems with different frames of reference.

System I encompasses the Equatorial Zone, the South Equatorial Belt and the North Equatorial Belt, and has a period of 10 hours and 14 minutes. System II covers all other Saturnian latitudes, excluding the north and south poles, and have been assigned a rotation period of 10 hr 38 min 25.4 sec. System III uses radio emissions to measure Saturn’s internal rotation rate, which yielded a rotation period of 10 hr 39 min 22.4 sec. This portrait looking down on Saturn and its rings was created from images obtained by NASA’s Cassini spacecraft on Oct. 10, 2013. Credit: NASA/JPL-Caltech/Space Science Institute/G. Ugarkovic Using these various systems, scientists have obtained different data from Saturn over the years. For instance, data obtained during the 1980’s by the Voyager 1 and 2 missions indicated that a day on Saturn was 10 hours 39 minutes and 24 seconds long.

In 2004, data provided by the Cassini-Huygens space probe measured the planet’s gravitational field, which yielded an estimate of 10 hours, 45 minutes, and 45 seconds (± 36 sec). In 2007, this was revised by researches at the Department of Earth, Planetary, and Space Sciences, UCLA, which resulted in the current estimate of 10 hours and 33 minutes. Much like with Jupiter, the problem of obtaining accurate measurements arises from the fact that, as a gas giant, parts of Saturn rotate faster than others. A Day On Uranus: When we come to Uranus, the question of how long a day is becomes a bit complicated. One the one hand, the planet has a sidereal rotation period of 17 hours 14 minutes and 24 seconds, which is the equivalent of 0.71833 Earth days. So you could say a day on Uranus lasts almost as long as a day on Earth. It would be true, were it not for the extreme axial tilt this gas/ice giant has going on.

With an axial tilt of 97.77°, Uranus essentially orbits the Sun on its side. This means that either its north or south pole is pointed almost directly at the Sun at different times in its orbital period. When one pole is going through “summer” on Uranus, it will experience 42 years of continuous sunlight. When that same pole is pointed away from the Sun (i.e. a Uranian “winter”), it will experience 42 years of continuous darkness. Uranus as seen by NASA’s Voyager 2. Credit: NASA/JPL Hence, you might say that a single day – from one sunrise to the next – lasts a full 84 years on Uranus! In other words, a single Uranian day is the same amount of time as a single Uranian year (84.0205 Earth years). In addition, as with the other gas/ice giants, Uranus rotates faster at certain latitudes. Ergo, while the planet’s rotation is 17 hours and 14.5 minutes at the equator, at about 60° south, visible features of the atmosphere move much faster, making a full rotation in as little as 14 hours.

A Day On Neptune: Last, but not least, we have Neptune. Here too, measuring a single day is somewhat complicated. For instance, Neptune’s sidereal rotation period is roughly 16 hours, 6 minutes and 36 seconds (the equivalent of 0.6713 Earth days). But due to it being a gas/ice giant, the poles of the planet rotate faster than the equator. Whereas the planet’s magnetic field has a rotational speed of 16.1 hours, the wide equatorial zone rotates with a period of about 18 hour. Meanwhile, the polar regions rotate the fastest, at a period of 12 hours. This differential rotation is the most pronounced of any planet in the Solar System, and it results in strong latitudinal wind shear. Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL In addition, the planet’s axial tilt of 28.32° results in seasonal variations that are similar to those on Earth and Mars. The long orbital period of Neptune means that the seasons last for forty Earth years.

But because its axial tilt is comparable to Earth’s, the variation in the length of its day over the course of its long year is not any more extreme. As you can see from this little rundown of the different planets in our Solar System, what constitutes a day depends entirely on your frame of reference. In addition to it varying depending on the planet in question, you also have to take into account seasonal cycles and where on the planet the measurements are being taken from. As Einstein summarized, time is relative to the observer. Based on your inertial reference frame, its passage will differ. And when you are standing on a planet other than Earth, your concept of day and night, which is set to Earth time (and a specific time zone) is likely to get pretty confused! We have written many interesting articles about how time is measured on other planets here at Universe Today. For example, here’s How Long Is A Year On The Other Planets? , Which Planet Has the Longest Day? , The Rotation of Venus , How Long Is A Day on Mars? and How Long Is A Day On Jupiter? .

If you are looking for more information, check out Our Solar System at Space.com Astronomy Cast has episodes on all the planets, including Episode 49: Mercury , and Episode 95: Humans to Mars, Part 2 – Colonists Share this: “Since it takes 58.646 Earth days for Mercury to rotate once on its axis – aka. its sidereal rotation period – this means that it takes just over 58 Earth days for Mercury to experience a single sunrise and sunset.” Sorry, Matt, but this is precisely incorrect, and I stopped reading at this point. 1) Sideral = stars; solar = Sol/The Sun. Mercury’s sidereal day/rotation period is indeed 58.646 Earth days. This means that it takes 58.646 Earth days for background stars (NOT the Sun) to rise, set, and then rise again. 2) “Days” are measured from sunrise to sunrise, not sunrise to sunset as you’ve indicated; if you think about the 24hrs of a Terran solar day you will see instantly that this is true.

3) Mercury’s solar day is heavily influenced by the Mercury’s speedy orbit around the sun; while Mercury rotates, it also revolves, leading to a Nabooan solar day of ~176 Earth days. This same effect of rotation + revolution is why sidereal and solar days are different in the first place — Earth’s solar day is ~24hrs, while its sidereal day is ~4min shorter — and is why the stars visible in our night sky locally change from season to season. 4) Finally, the effect of revolution + Mercury’s noticeably elliptical orbit + rotation leads to some bizarre timing when it comes local sunrise, sunset, noon, and midnight in various places on the planet as well. In some places, one ends up with Sol crossing overhead three separate times between local sunrise & sunset; in others “Sunrise” is spread out over weeks (Earth reckoning) as Sol rises above the horizon, then sets completely, then rises again to cross the sky, only to perform the same dance in reverse upon “Sunset” (set, rise again, set again). Thought we maybe discussed this once before, somewhere….

Planets - Zoom Astronomy Your age on the Planets The Planets (plus the Dwarf Planet Pluto) Our solar system consists of the sun, eight planets, moons, many dwarf planets (or plutoids), an asteroid belt, comets, meteors, and others. The sun is the center of our solar system ; the planets, their moons, a belt of asteroids , comets , and other rocks and gas orbit the sun. The eight planets that orbit the sun are (in order from the sun): Mercury , Venus , Earth , Mars , Jupiter , Saturn , Uranus , Neptune . Another large body is Pluto , now classified as a dwarf planet or plutoid. A belt of asteroids (minor planets made of rock and metal) lies between Mars and Jupiter. These objects all orbit the sun in roughly circular orbits that lie in the same plane, the ecliptic (Pluto is an exception; it has an elliptical orbit tilted over 17° from the ecliptic).

Easy ways to remember the order of the planets (plus Pluto) are the mnemonics: "My Very Excellent Mother Just Sent Us Nine Pizzas" and "My Very Easy Method Just Simplifies Us Naming Planets" The first letter of each of these words represents a planet - in the correct order. The largest planet is Jupiter. It is followed by Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury, and finally, tiny Pluto (the largest of the dwarf planets). Jupiter is so big that all the other planets could fit inside it. The Inner Planets vs. the Outer Planets The inner planets (those planets that orbit close to the sun) are quite different from the outer planets (those planets that orbit far from the sun). The inner planets are: Mercury, Venus, Earth, and Mars. They are relatively small, composed mostly of rock, and have few or no moons. The outer planets include: Jupiter, Saturn, Uranus, Neptune, and Pluto (a dwarf planet). They are mostly huge, mostly gaseous, ringed, and have many moons (again, the exception is Pluto, the dwarf planet, which is small, rocky, and has four moons).

Temperatures on the Planets Generally, the farther from the Sun, the cooler the planet. Differences occur when the greenhouse effect warms a planet (like Venus) surrounded by a thick atmosphere. Density of the Planets The outer, gaseous planets are much less dense than the inner, rocky planets. The Earth is the densest planet. Saturn is the least dense planet; it would float on water. The Mass of the Planets Jupiter is by far the most massive planet; Saturn trails it. Uranus, Neptune, Earth, Venus, Mars, and Pluto are orders of magnitude less massive. Gravitational Forces on the Planets The planet with the strongest gravitational attraction at its surface is Jupiter. Although Saturn, Uranus, and Neptune are also very massive planets, their gravitational forces are about the same as Earth. This is because the gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of the planet's radius squared. A Day on Each of the Planets A day is the length of time that it takes a planet to rotate on its axis (360°). A day on Earth takes almost 24 hours.

The planet with the longest day is Venus ; a day on Venus takes 243 Earth days. (A day on Venus is longer than its year; a year on Venus takes only 224.7 Earth days). The planet with the shortest day is Jupiter ; a day on Jupiter only takes 9.8 Earth hours! When you observe Jupiter from Earth, you can see some of its features change. The Average Orbital Speed of the Planets As the planets orbit the Sun , they travel at different speeds. Each planet speeds up when it is nearer the Sun and travels more slowly when it is far from the Sun (this is Kepler's Second Law of Planetary Motion ). The Planets in Our Solar System Planet (or Dwarf Planet) In 2005, a large object beyond Pluto was observed in the Kuiper belt. A few astronomers think that there might be another planet or companion star orbiting the Sun far beyond the orbit of Pluto. This distant planet/companion star may or may not exist. The hypothesized origin of this hypothetical object is that a celestial object, perhaps a hard-to-detect cool, brown dwarf star (called Nemesis ), was captured by the Sun's gravitational field.

This planet is hypothesized to exist because of the unexplained clumping of some long-period comet's orbits. The orbits of these far-reaching comets seem to be affected by the gravitational pull of a distant, Sun-orbiting object. Planet Activities and Quizzes Jupiter Facts - The Planet Jupiter - Jupiter For Kids Download Questions about Jupiter (all answers found on this page) Jupiter is the giant of the Solar System , with a mass more than 300 times the mass of the Earth and is called after the ancient Roman sky-god, Jupiter, known to the Greeks as Zeus. Jupiter has a diameter of 88,700 miles, or 142,750 kilometres. Jupiter is the fifth planet in order from the Sun and is about 483 million miles, or 777 million kilometres from the Sun . Figure 1 shows the planets in order but the distances are not to scale. The Earth is much closer to the Sun than it is to Jupiter. Distances from the Sun are measured in Astronomical Units (AU).

The Earth is the standard unit, and is one AU from the Sun, so an AU equals 150 million kilometres (93 million miles), the distance of the Earth from the Sun. Figure 2 shows the distance from the sun of the first five planets, Mercury 0.4 AU , Venus 0.7 AU , Earth 1AU , Mars 1.5 AU and Jupiter 5.2 AU . Figure 1: Distance from Sun showing how The Earth is closer to the Sun than it is to Jupiter. All planets in the Solar system orbit round the Sun. The Earth takes just over 365 days, so the Earth’s year is 365 days. It takes Jupiter 11.9 of the Earth’s years to make its orbit round the Sun. Although Jupiter’s orbit, and therefore its year, is so much longer than the Earth’s, its day is much shorter. The Earth turns on its own axis, turning away from the Sun and so giving us day and night, once every 24 hours. Jupiter spins round much faster, turning on its axis once every 9.84 hours!

This fast spinning gives rise to very strong weather patterns in the clouds which surround the planet and so its appearance changes rapidly. Jupiter is the stormiest planet in the Solar System. There is a permanent, but ever-changing whirlpool of storms, known as Jupiter’s Great Red Spot which can be seen using a telescope. The Red Spot was first seen by Robert Hooke in 1664 . The gas giants are entirely composed of dense layers of gas. Jupiter is made of hydrogen, helium, methane and ammonia. The cloudy sphere has bright belts on it which change their shape. Figure 2: Jupiter’s Great Red Spot Figure 3: Jupiter showing its bands, with the Great Jupiter can be seen without a telescope and so was known in the ancient world, but it was not until the invention of telescopes that astronomers were able to see Jupiter’s moons. There are 64 moons in total, four of which are large enough to be easily observed with a small telescope. The Solar System: Venus | The Institute for Creation Research The Solar System: Venus Resources › Physical Sciences Resources › Astronomy For millennia, people have enjoyed the sight of the “evening star” shining brightly in the western sky shortly after sunset.

Outshining all other stars, this remarkable beacon seems to brighten to unbelievable glory as twilight fades to night. It rises higher night after night and then stops and begins to sink lower each evening until it vanishes below the horizon. Sometime later, it reappears just before sunrise in the eastern sky as the bright “morning star.” What did the ancient astronomers think about this magnificent object and its peculiar celestial dance? They called it “Venus,” after the Roman goddess of love and beauty.1 Physical Properties With modern technology, we have learned a great deal about Venus. It’s not a “star” at all, but a planet—a small rocky world that shines only by reflected sunlight.2 In fact, Venus is about the same size as Earth.3 So when we look at Venus, it’s fun to think that this is also how tiny Earth would appear if viewed from Venus. The composition of Venus is also similar to Earth, and its orbit is physically closest to Earth’s of all the planets. For these reasons Venus is sometimes referred to as “Earth’s sister” or “Earth’s twin.”4 But there are far more differences than similarities.

An examination of the surface of Venus has proved quite challenging because Venus is permanently enshrouded in thick clouds of sulfuric acid and toxic sulfur dioxide, masking all surface features. The atmosphere is comprised mainly of carbon dioxide and is the thickest atmosphere of the four terrestrial planets. At the surface, Venus has a crushing air pressure that is 92 times greater than Earth’s! This thick atmosphere acts like a blanket, trapping solar energy and warming the planet to unbelievable temperatures. And since Venus orbits 26 million miles closer to the sun than Earth does, Venus already endures nearly twice the solar energy. The greenhouse effect causes the surface temperature of Venus to approach 900°F—the hottest of any planet in our solar system. In 1990, the NASA spacecraft Magellan was inserted into orbit around Venus and began systematically mapping the surface using radar. Since radar is not blocked by clouds, Magellan was able to map the topography of Venus in unprecedented detail. The four-year-long mission revealed that Venus has many of the same geological features found on Earth, including mountains, valleys, canyons, volcanos, lava flows, craters, and plains.

Venus also has two major “continents”—Ishtar Terra and Aphrodite Terra. But since there is no liquid water on Venus, these “continents” are recognized only by their high elevations. Venus also has geological features not found on Earth, such as arachnoids, novae, tesserae, coronae, and pancake domes. Arachnoids are regions where the terrain has been folded and broken into a gossamer-looking structure resembling a spider web. Novae are “radially fractured centers” between 60 and 200 miles in diameter. Sixty-four novae have been discovered on Venus.5 Tesserae are complex ridged terrains found on plateaus. “Corona” is from the Latin meaning “crown.”6 They are oval-shape features thought to be produced by plumes of upwelling magma that cause the surface to bulge and then collapse in the center, forming a crown-like ring. Pancake domes are similar in most respects to shield volcanoes on Earth, such as Mauna Loa in Hawaii. However, pancake domes are flatter and broader than their terrestrial counterparts. Venus has no moons and virtually no magnetic field.

Such similarity, yet with differences, is consistent with the nature of God. God is the source of creativity and has created a diversity of objects within the universe, and yet there are similarities since the entire universe was created and is upheld by the same God. Differences and similarities are seen in the biological world, the world of particle physics, and in the solar system as well. But in the secular view, how can we make sense of this? Earth and Venus are nearly identical in size and bulk composition and have similar orbits. In the secular view, they have a similar history too. So why would Earth’s “sister” be so radically different from Earth? There are secular speculations for such things—but such diversity is expected in the Christian worldview. A Day on Venus Venus has the most circular orbit of any planet in the solar system. Its axial tilt is only three degrees, so there are no seasons on Venus. Since it orbits closer to the sun than Earth does, Venus orbits faster and completes a circuit every 7.4 months. But its day is much longer than Earth’s. Venus rotates once every eight months, so its day is actually longer than its year.

This is the sidereal day—the rotation of Venus relative to the stars.7 What is even more intriguing is that Venus rotates backward. All eight planets orbit the sun counterclockwise, as viewed from the solar system’s North Pole. Most of the planets also rotate counterclockwise,8 but Venus is the exception.9 On Venus, the sun would rise in the west and set in the east—although it would be difficult to see the sun in such overcast skies. Secularists do not have a good explanation for the backward rotation of Venus. In the secular scenario, the solar system is supposed to have formed from the collapse of a rotating nebula. The natural expectation of this would be that all planets would rotate in the same direction at about the same rate, and they would all have very little axial tilt. Venus is the worst offender to this concept, since it rotates exactly the opposite of what the evolutionary models require. But we expect such diversity in the biblical view. The backward rotation of Venus causes its solar day to be much shorter than its sidereal day—a unique phenomenon in the solar system.

Recall that the solar day is the average time from one sunrise to the next as viewed from a planet’s surface (e.g., 24 hours for Earth). This is different (and normally slightly longer) from the sidereal day because planets orbit the sun and not the stars. Since Venus rotates in the opposite direction, its solar day is reduced to 3.8 months. Strangely, this is shorter than Mercury’s solar day, even though Venus physically rotates slower than Mercury. Phases and the Nature of the Solar System Venus is a great target for telescope beginners. Its brightness makes it easy to find, and its size and proximity to Earth allow viewers to discern its shape through even a small, inexpensive telescope. Although the clouds on Venus prevent observations of any surface features, observers will immediately notice that Venus has phases; it is not uniformly illuminated, but appears bright on one side and dark on the other. Viewers sometime describe it as a tiny craterless “moon,” since the moon is the only other object that we readily recognize as going through phases.

Just like the moon, Venus goes through new, crescent, quarter, gibbous, and full phases.10 And like the moon, these phases make it obvious to the eye that Venus is spherical, not a flat disk. But there are three differences in the phases of Venus compared to the moon. First, the moon takes roughly one month to go through its phases, whereas Venus takes over 19 months. Since Venus orbits the sun faster than Earth does, it physically overtakes and passes the Earth every 19 months. This is called the synodic period of Venus. Since the phase of Venus as seen from Earth depends on the relative positions of Earth, Venus, and the sun, phases correlate with the synodic period. Second, whereas the moon remains approximately the same apparent size as it goes through its phases, Venus does not. Venus appears very small when in its gibbous phase (nearly full) and appears very large when in its crescent phase.11 This is because Venus orbits the sun, not the Earth. Hence, when Venus is nearly in-between the sun and Earth and we are viewing only a thin sliver of the illuminated side, Venus is nearly as close to Earth as it gets.

Conversely, when Venus is on the far side of the sun, we see it nearly fully illuminated. Galileo was the first person to observe and document this effect. His telescopic observations of Venus led him to realize that planets orbit the sun—not the earth. This was in contrast to the prevailing scientific view of the day. The earth-centered (geocentric) solar system predicts that Venus will only appear as a crescent. The sun-centered (heliocentric) model can make sense of the phases of Venus and their correlation with its apparent size. Finally, the phases of Venus (and Mercury) are reversed relative to the moon. In other words, when the moon is illuminated on the right side (toward the western horizon), it is in a waxing phase and will appear more illuminated on the following night. But when Venus is illuminated on the right side, it is in a waning phase and will appear less illuminated over the following weeks. Both Venus and the moon orbit in the same direction. So how can this be? The difference is because Venus orbits the sun, whereas the moon orbits Earth. So when the moon is in-between Earth and the sun, it is moving to the left (eastward).

But when Venus is in between the sun and Earth, it is moving to the right (westward). From our perspective on Earth, Venus stands out as a pure white light, superior in splendor and luminance. Venus is mentioned in Scripture as the “morning star,” where its brilliance is used as a symbol for Christ ( Revelation 2:28 ; 22:16).12 None of the other nighttime stars can compete with Venus, so it is a fitting symbol of the beauty and glory of our Lord. References Venus is the second-brightest regular object in our night sky. Only the moon is brighter. Venus is not a star in the modern sense of the word. However, the ancient term for star (aster in Greek, kowkab in Hebrew) includes both stars and planets. A planet is a “wandering star”—a star that moves relative to the majority of fixed stars. Venus is 95 percent as large as Earth in diameter. Though they do have the same Father ( James 1:17 ), they cannot be “twins” because Earth is three days older than Venus ( Genesis 1:1 , 14-19).

Krassilnikov, A. S. and J. W. Head. 2003. Novae on Venus: Geology, Classification, and Evolution. Journal of Geophysical Research: Planets (1991-2012). 108 (E9): 1-48. Coronae are found only on Venus and Uranus’ moon Miranda. See the Mercury article for a discussion of sidereal versus solar days: Lisle, J. 2013. The Solar System: Mercury . Acts & Facts. 42 (8) 10-12. This is relative to the North Pole of the solar system. Alternatively, we could define the North Pole of a planet as the pole under which the planet rotates counterclockwise. By this definition, all planets rotate in the same direction and Venus is merely “upside down.” There is no physical difference between Venus being tilted 3° and rotating backward (clockwise), as opposed to Venus being tilted 177° and rotating forward (counterclockwise). Both conventions are used in astronomy.

Since the planet Uranus is tilted 97°, it too could be considered a backward-rotator with a tilt of 83°. However, since this is nearly a right angle, it makes little difference. The outer planets can only be seen in gibbous and full phases. This is because quarter and crescent phases require the planet to be closer to the sun than the observer is. This can never occur for an outer planet as seen from Earth. This effect is also visible in the planet Mercury for the same reason. However, the effect is much less noticeable on Mercury since its distance from Earth does not vary as much. Also, Mercury is much smaller than Venus and closer in angle to the sun, making observations of its apparent diameter far more difficult. In some English translations, Lucifer is called the morning star in Isaiah 14:12 . It may bother some people that the same symbol is used for Christ, but Isaiah 14:12 may simply indicate that Lucifer was one of the most glorious angels before he rebelled.

Satan attempts to parrot Christ in some ways—Christ is the Lion of Judah ( Revelation 5:5 ), and Satan prowls about as a roaring lion ( 1 Peter 5:8 ). We note that the word “star” does not appear in the Hebrew text of Isaiah 14:12 . “Son of the morning” or “son of the dawn” appears to be a more literal translation from the original text. * Dr. Lisle is Director of Physical Sciences at the Institute for Creation Research and received his Ph.D. in Astrophysics from the University of Colorado. Cite this article: Lisle, J. 2013. The Solar System: Venus. Acts & Facts. 42 (9): 10-12. How Long Is A Year On Uranus? How Long is a Year on Uranus? Our Planets Home >> Articles >> How Long is a Year on Uranus? 1 year on Earth is the length of time that it takes Earth to orbit the sun.

Earth’s orbit takes just over 365 days (the ‘extra’ bit on top of the 365 days is why we have a leap year every four years, where an extra day is added onto February). Uranus is much further away from the sun, and it takes 84.3 Earth years for Uranus to complete its orbit - this is one ‘year’ for Uranus. This means that Uranus is travelling around the sun at a speed of 15,290 miles per hour (24,607 km per hour). The other planets also have different lengths in their years. For example, Mercury’s year is only 88 Earth days! This is the shortest orbit of all of the planets, which makes sense since Mercury is the closest planet to the sun (so it has a shorter distance to go). You may be surprised to know that the lengths of the days on different planets also vary a lot, and some of them have days that are longer than their years! 1 day on Earth is 24 hours. This is the amount of time that it takes the Earth to rotate completely on its axis.

Venus’ day is the equivalent of 243 Earth days, while it’s year is 225 Earth days. This means that Venus’ day is longer than it’s year! It is orbiting the sun faster than the time it takes to completely rotate on its axis. On Uranus, a day takes nearly 18 Earth hours. This means that while Uranus’ day is shorter than Earth’s, its year is significantly longer! This means that Uranus is rotating very fast when compared to Earth, and orbiting the sun very slow (because it is so far away). There are many other ways in which Uranus is different to Earth, such as gravity. If you could stand on Uranus (which you can’t, not least because Uranus is made of gas!), the gravity would be 89% as strong as the gravity on Earth. So if you weighed 100kg (or 100lb) on Earth, you would weigh 89kg (or 89lb) on Uranus. To give you an idea of what this would feel or look like, the gravity on the Moon is 83% as strong as Earth.

So you would be slightly more ‘weighed down’ than you would be on the Moon. You may have seen videos or pictures of astronauts ‘bouncing’ on the Moon - you would be a little bit less bouncy than this on Uranus. Rotation Period and Day Length Rotation Period and Day Length (If you are math-phobic, refer to The Use of Mathematics in My Lecture Classes ) (Note added Mar 30, 2015: A newly determined rotation rate for Saturn is 10 seconds longer than the value used in the tables below, but since the new rate has an uncertainty of 45 seconds, there is no good reason to change the values shown here.) The Sidereal Period of Rotation vs. the Synodic Period of Rotation As a planet rotates around its axis, the stars appear to move around a projection of the planet's axis into space. The time required for the stars to move once around their paths is called the sidereal period of rotation, or the rotation period of the planet. While the planet rotates, it is also moving around the Sun.

This changes the apparent position of the Sun among the stars, and as a result, it does not move around the sky in quite the same period of time that the stars do. Depending upon whether the rotation of the planet is direct (in the same direction as its orbital motion) or retrograde (in the opposite direction as its orbital motion), the time that the Sun takes to go once around the sky, which is called the synodic period of rotation, or the length of the day, may be longer or shorter than the sidereal period of rotation. Table 1 shows the rotation period and the length of the day for the Moon, and the planets. As you can see, for most of the bodies, the two times are very similar, but for objects which have slow rotation periods, such as the Moon, Mercury and Venus, there is a large difference between the two time periods.

Body (the nearly sideways rotation of) Pluto Sidereal Period 23 hr 56 min 4.1 sec 27.322 days 24 hr 37 min 22.66 sec 9 hr 55 min 30 sec 10 hr 32 min 35 sec - 17 hr 14 min 24 sec 16 hr 6.6 min - 6 days 9 hr 17.6 min Synodic Period = "Day" 24 hr 0 min 0 sec 29.53 days 24 hr 39 min 35.24 sec 9 hr 55 min 33 sec 10 hr 32 min 36 sec - 17 hr 14 min 23 sec 16 hr 6.6 min - 6 days 9 hr 17.0 min Table 1: Comparison of Sidereal and Synodic Periods (some links lead to more detailed discussions; others will, at a later date) Retrograde Rotation All of the planets orbit, or revolve around the Sun in the same eastward direction.

Most of them also rotate around their axes in that same direction. Venus, Uranus and Pluto, however, rotate in the opposite direction, and if we need to do any arithmetic involving their rotation, such as comparing their rotation rate to their day length, we have to distinguish between DIRECT rotation, which is in the same direction as the orbital motion, and RETROGRADE rotation, which is in the opposite direction. To accomplish this we define the rotation period as the time that it takes for the planet to turn once around its axis TO THE EAST, causing the stars to turn around the sky to the west. If the planet rotates in the opposite direction, causing the stars to turn around the sky in the opposite direction, we would have to run time backwards in order to see a westward motion for the stars. As a result, the rotation period of a planet which has a retrograde rotation is a negative number, as shown in the table for the three planets which have such a rotation. Keep in mind that even though some planets have retrograde ROTATION, they ALL orbit or REVOLVE around the Sun in the same direction. For additional discussion of retrograde motion in general or retrograde rotation in particular, refer to Retrograde Motion .

The tilts of the planets Most planets' rotation is to the east, as for the Earth. Some planets (Venus, Uranus and Pluto) rotate to the west if the North Pole is defined as the one 'on top' of the planet (above the plane of our orbit). For those planets we can say they are upside down (tilt greater than 90 degrees), or that they rotate backwards (tilt = a negative number) relative to their orbits. Cautionary Notes Because the rotation period of the Earth is almost the same as the length of its day we sometimes get a bit sloppy in discussing the rotation of the sky, and say that the stars rotate around us once each day. In a similar way it is not unusual for careless people to mix up the rotation period of a planet with the length of its day, or vice-versa. So you might read that Mars has a day length of 24 hours and 37 minutes, which is actually its rotation period, or that Venus rotates in 117 days, which is actually the length of its day.

Perhaps in the case of Mars an error of a couple of minutes is not terribly important, but saying that Venus rotates in 117 days is not even close to the actual value of 243 days. So unless you want to risk making serious errors, you should be sure you know what you mean when you state either value. There is also a small deliberate error in the use of the terms "sidereal time" and "year" on this page, because astronomers normally use sidereal time to measure the westward motion of the Earth's sky as defined by the motion of the Vernal Equinox, not the motion of the stars. Because of precession, the Earth's stellar and sidereal days differ by about 8 milliseconds, and the length of the year (shown as 365.2422 days) differs from the Earth's orbital period by about 20 minutes. These errors are small compared to the numbers otherwise discussed on this page, and apply only to the Earth, so it seemed best to ignore them in the interest of simplicity. Explaining the Difference Between Rotation and Day Length As shown in the table the rotation period and day length are nearly identical for all of the outer planets.

In fact for most of them the values are so nearly identical that they are the same, to the accuracy shown here. For the Moon and the inner planets, however, the situation is quite different. The Earth and Mars, which rotate relatively quickly, have only a few minutes difference between the their rotation period and the day length, but for the Moon, Venus and Mercury, the difference between the two values is quite large. For the Moon the difference is two days ï¿½ not enough to make the day appear tremendously different from the rotation period, but enough to be confusing if the reason for the difference is not understood ï¿½ and for Mercury and Venus the difference between the two values is so large that their rotation periods appear, at first glance, to be completely unrelated to the lengths of their days. To explain why the day length, or synodic period of rotation is different from the sidereal period of rotation, we consider how a given place moves around a planet, and the way in which this changes its view of the sky during one rotation period. In the diagram below the four blue dots on the right represent the position of the planet at four times, separated from each other by a third of a rotation period.

The number of rotations that the planet has made is indicated by the numbers to the right of each dot. The white dot shows how the position of a specific place on the planet changes as the planet rotates to the east (counter-clockwise in this diagram), and the large yellow dot on the far left represents the position of the Sun. The sizes of the Sun and planet and the angle that the planet moves through during one rotation have been exaggerated to make it easier to see what is happening. The movement of a planet during one rotation. The planet's movement around the Sun causes the Sun to appear to move around the sky. Each degree that the planet moves around the Sun causes the Sun to appear to move a degree around the planet. At the beginning of the rotation, shown by the blue dot at the bottom of the diagram, the place we are following is on the side of the planet facing the Sun, so that it is noon with the Sun more or less overhead at that place. As the planet moves around the Sun, that place moves counter-clockwise around the planet, as shown by the changing position of the white dot.

At the top position the planet has made one full rotation, and the planet and the white dot are facing in the same direction as at the beginning, as indicated by the horizontal lines extending to the left from the starting and ending positions for the planet. If any stars were visible they would have made exactly one trip around the sky during the one rotation period that has passed. For the Sun, however, the situation is different. As shown by the diagonal line connecting the end position for the planet to the Sun, the planet has moved around the sun by some angle A (shown on the left near the Sun), and as a result the Sun appears to have moved through that same angle A (shown on the right near the planet) relative to the stars. Although the stars have gone all the way around the sky, the Sun is still a little shy of completing its journey, and needs a little more time to make up for the extra angle that it still needs to cover.

Because of this the rotation period (the time for the stars to go around) differs from the day (the time for the Sun to go around) by a small amount of time (approximately, the time that the planet takes to turn through an angle equal to the angle A that it moved around the Sun). The Rotation Period of the Earth To see how this works, consider the case of the Earth. The Earth goes around the Sun in one year, or approximately 365 1/4 days. The number of degrees in a circle is 360 degrees, which is about the same as the number of days in a year, so the angle that the Sun seems to move relative to the stars during one rotation is approximately one degree. To calculate how long it takes for the Earth to rotate through an angle of one degree, we divide the length of a day, 24 hours or 1440 minutes, by the 360 degrees it turns through during that rotation, obtaining a rotational speed of 4 minutes per degree.

Since the Sun's motion differs from the stars' motion by one degree, and it takes 4 minutes for the Earth to turn through one degree, it takes the Sun 4 minutes longer to go around the sky than it takes for the stars to do so, and the rotation period of the Earth is 4 minutes less than the length of its day. Since we define a day as having exactly 24 hours, the rotation period of the Earth is 23 hours 56 minutes, as shown in the table. The Rotation Periods of the Outer Planets For the outer planets we can use the same sort of calculation that we just did for the Earth, taking advantage of the fact that they have much longer orbital periods, so the number of rotations in a year is much larger and the distance they move during one rotation is correspondingly smaller. For Mars, the year is nearly twice as long as ours, 686.98 days, and the rotation period is a little longer than ours, 24 hours 37 minutes 22.66 seconds (this is often erroneously listed as the length of the day).

Dividing the rotation period into the year we find that Mars rotates 670 times in a year, moving around the Sun about half a degree during each rotation. Since Mars rotates at about the same rate that we do, it would take about 2 minutes to make up for this half-degree motion; so on Mars the day must be about 2 minutes longer than the rotation period. These calculations are rounded off considerably, so the results are only approximate; but if the calculations were accurately done the results would be reasonably accurate, as well. For planets which are even further out, the motion around the Sun is even smaller and the time required to compensate for it is only a few seconds. For Jupiter the difference between the rotation period and the length of the day is about 3 seconds; and for Saturn, Uranus and Neptune, the difference is about 1 second. Even for Pluto, which has a much longer rotation rate than the Jovian planets, the difference between the rotation period and the day is less than 40 seconds ï¿½ a small difference compared to its rotation period of more than six days.

As a result, the day length and rotation period are about the same, and we often treat them as being the same (just as we often do, though not as accurately, for the Earth). The above technique works well for the planets with rotation rates which are rapid compared to their orbital periods, so that they rotate hundreds, thousands, or even tens of thousands of times in each orbit. But for objects which rotate very few times in an orbit the angle A is very large, which means that it takes quite a while for the planet to rotate through that extra angle, and the difference between the day and the rotation period can become surprisingly large, as shown below for the Moon. The Rotation Period and Day Length of the Moon Since the Moon moves around the Sun with the Earth, the Sun moves the same one degree per day in the lunar sky as it does during the Earth's rotation. But while the Earth rotates in about one day, the Moon takes more than 27 days to rotate, so during one lunar rotation the Sun moves over 27 degrees relative to the stars. To make up for this, the Moon has to rotate more than two days longer, as can be seen by comparing its rotation period to its day length.

The 2.2 day difference between the periods seems extreme, but the basic idea is the same as for the Earth; it's just that since the Moon rotates so slowly that (1) the Sun moves much further during one lunar rotation than during one Earth rotation, and (2) the Moon takes longer than the Earth to make up for any given solar motion. Each of these factors increases the four minute difference between the Earth's rotation and day length by the 27.3 times slower motion of the Moon, for a combined increase of 27.3-squared, or nearly 750 times. So the four minute difference between day length and rotation period becomes 4 times 750, or 3000 minutes, which is a little over two days. Unfortunately, that's not the end of the calculation, because during the time the Moon must rotate to make up for its motion around the Sun it continues to move around the Sun, causing another two degree difference between the solar and stellar motions, which takes another four hours to make up (4 minutes per degree for the Earth, times two degrees to make up, times 27 times slower rotation for the Moon).

And during that four hours the Moon moves another sixth of a degree around the Sun, so for really precise results we'd have to keep doing this, with smaller and smaller times and angles, until the difference was too small to bother with. A More Accurate Calculation For the Moon, we might be satisfied with just the two-step calculation shown above, and not bother with smaller and smaller corrections. But if we wanted accurate results for Mercury and Venus, which rotate even more slowly and have shorter orbital periods, we couldn't get away with just one or two corrections; half a dozen or more might be needed, depending upon the accuracy desired. So for those planets we need a different way of doing the calculations; but fortunately, there is a relatively simple way of calculating the difference between rotation period and day length, which can be done as accurately as we want by simply using accurate numbers to do the arithmetic. In one year the planet rotates a certain number of times, and the stars go around the sky that number of times.

If the planet were stationary relative to the Sun, so that the Sun was fixed in the sky relative to the stars, it would rise and set the same number of times as the stars, but during one year the planet moves once around the Sun, and as a result the Sun moves once to the east among the stars. If the planet has direct rotation, as most do, so that the stars move westwards across the sky, the Sun's eastward motion relative to the stars is backwards, so it goes around the sky one less time, and The number of days in a year = the number of rotations - 1. If the planet has retrograde rotation the stars will move across the sky to the east, instead of to the west, and the Sun's eastward motion will result in its crossing the sky one more time than the stars in one year. However, since we treat this kind of rotation as having a negative rotation period, the larger negative number is still one less than the number of rotations. This equation can, therefore, be applied to all the planets, regardless of how they rotate. The table below shows the results of using this method for all the planets and the Moon. The most interesting result is for Mercury.

Its slow rotation and fast orbital motion cause a huge difference between the day and rotation period, which differ by a factor of three, more than for any other planet. But what is really striking is that the rotation period is exactly 2/3 of the orbital period, and the day is exactly two orbital periods, so that one side of Mercury faces the Sun for a whole year, then the other side for the next year. Even more surprisingly, as discussed in The Rotation of Mercury , when Mercury is closest to the Sun at perihelion, its orbital and rotational motion are nearly identical, so that for more than a week the same side of the planet faces an apparently motionless Sun, almost as if it always kept the same side to the Sun, as we used to believe. Object All About Venus :: NASA Space Place Tweet What is Venus like? Even though Venus isn't the closest planet to the sun, it is still the hottest. It has a thick atmosphere full of the greenhouse gas carbon dioxide and clouds made of sulfuric acid. The gas traps heat and keeps Venus toasty warm. In fact, it's so hot on Venus, metals like lead would be puddles of melted liquid. Venus looks like a very active planet.

It has mountains and volcanoes. Venus is similar in size to Earth. Earth is just a little bit bigger. Venus is unusual because it spins the opposite direction of Earth and most other planets. And its rotation is very slow. It takes about 243 Earth days to spin around just once. Because it's so close to the sun, a year goes by fast. It takes 225 Earth days for Venus to go all the way around the sun. That means that a day on Venus is a little longer than a year on Venus. Since the day and year lengths are similar, one day on Venus is not like a day on Earth. Here, the sun rises and sets once each day. But on Venus, the sun rises every 117 Earth days. That means the sun rises two times during each year on Venus, even though it is still the same day on Venus! And because Venus rotates backwards, the sun rises in the west and sets in the east. Just like Mercury, Venus doesn’t have any moons. Venus' Merit Badges

Question: Which planet's day is longer than its year?
Answer: Venus